The true number messed you up so much you can’t recall it any more.

It’s extremely rare. Big breaking updates are normally shown in the arch news. Usually they just require a command or two to remove a conflicting package before the update. I think there’s been a few in the last year, but on the flip side I never got a clean distro update on anything but Debian and they usually took a lot more effort to clean up.

Where it may be “unstable” is if a specific program updates (upstream) with some major change or other, whereas another distro might hold off a while.

“unstable” as in changing regularly. Not in any way to do with how reliable it is (as another comment mentioned, that’s a better way to differentiate).

I’ve had far fewer problems updating arch (once I had a clean system anyway) than I ever did trying to move through distribution updates on various other more “standard” ones.

Nah, I looked at it and it doesn’t interest me. I like arch because, contrary to popular belief, it is quite stable (as in non crashing, not package versions) if you only install exactly what you need. I had way more stability issues on the more standard distros since they had so much extra stuff. Debian for servers every day though.

Nix looks interesting in theory, but is a lot of work and too opinionated for me. Far from an expert though and have nothing against those that like it or any other distro.